Abstract
Diseases that should be considered in the differential diagnosis of Hashimoto's thyroiditis (HT) include subacute thyroiditis and Reidle's thyroiditis, Graves' disease, euthyroid sick syndrome, goiter, hypopituitarism, lithium-induced goiter, simple (non-toxic) goiter, thyroid lymphoma, toxic nodular goiter, and types I and II polyglandular autoimmune syndrome. The characteristic diagnostic clinical, biochemical, imaging (sonographic), and histological/cytological features of HT will help make a differential diagnosis. This chapter explores the differential diagnosis of Hashimoto's disease.
TopThyroiditis
Hashimoto's thyroiditis should be distinguished from other forms of thyroiditis.
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Subacute granulomatous thyroiditis: It is a self-limiting painful disorder of the thyroid. Clinical examination, elevated erythrocyte sedimentation rate (ESR), elevated thyroglobulin (Tg) level and decreased radioactive iodine (RAI) uptake confirms the diagnosis.
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Acute suppurative thyroiditis: It is a rare infectious condition of the thyroid.
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Reidle’s thyroiditis: It is a fibrosing disorder of thyroid characterized by hypothyroidism and hypocalcemia, and diagnosis is made by histo-pathology.
TopThyroid Neoplasm
A thyroid tumor must also be considered in the differential diagnosis of Hashimoto's disease, particularly if there is rapid growth of the gland or persistent pain. The diffuse nature of autoimmune thyroiditis, the characteristic hypothyroidism and involvement of the pyramidal lobe are usually sufficient for differentiation. It is still uncertain whether FNA is indicated. However, it must be remembered that lymphoma or a small-cell carcinoma of the thyroid can be and has been mistaken for Hashimoto's thyroiditis. Clusters of nodes at the upper poles strongly suggesting papillary thyroid carcinoma (PTC) may disappear when thyroid hormone replacement therapy is given. However, a sufficient number of patients with both thyroiditis and tumor have been recorded. Thus, one diagnosis in no way excludes the other. Papillary thyroid carcinoma with Hashimoto's thyroiditis is characterized by female predominance, multi-focality, no extra-thyroid extension, no lymph node metastasis and better recurrence-free survival (Zhang, 2012; Fiore, 2011; Krysiak, 2011). Thyroid lymphoma must always be considered if there is continued (especially asymmetric) enlargement of a Hashimoto's gland, or if pain, tenderness, hoarseness, or nodes develop. Thyroiditis is a risk factor for thyroid lymphoma, although the incidence is very low. Distinguishing thyroid lymphoma from Hashimoto's thyroiditis is sometimes quite difficultin cytology. Flow cytometry, immune histochemistry or polymerase chain reaction (PCR) should aid in diagnosis (wozniak, 1999; Miller, 1991). Reverse transcription-polymerase chain reaction (RT-PCR) detecting the mono-clonality of immunoglobulin heavy chain mRNA is useful for differentiation between the two (Tanako et al., 2000).